Conventionally, the glass bulb 1 of a cathode-ray tube comprises a funnel portion 2, anode terminal 3 mounted on the funnel portion, and conducting layer 4 deposited on the inside of the funnel portion 2. The anode terminal 3 is overlapped by the conducting layer 4, and electrically connected to the electrode 12 of an electron gun 8 having conducting layers 5 and 6 and conducting metal 7, as shown in FIG. 1. To the inside of the panel 9 of the glass bulb 1 is attached a fluorescent film 10 and metal back 16 electrically connected to the anode terminal 3. The metal back 16 comprises a conducting panel 15, spring 17 for holding a mask, mask frame 13, conducting metal strip 14, and the conducting layer 4.
The equivalent circuit of this conventional cathode-ray tube is shown in FIG. 3A. A high voltage from the anode terminal 3 is applied through a high resistance body 5 (resistance R in FIG. 3A) to the electrodes 12 of an electron gun 8. In this case, there occurs frequently an electric discharge between the electrodes due to possible foreign matters such as dust, so that a discharging current of a high peak value as shown in FIG. 4A or 4B may flow to damage the circuit elements connected to the electrodes of the electron gun 8.